Amyloid fibrils of transthyretin (TTR) consist of full-length TTR and C-terminal fragments starting near residue 50. However, the molecular mechanism underlying the production of the C-terminal fragment remains unclear. Here, we investigated trypsin-induced aggregation and urea-induced unfolding of TTR variants associated with hereditary amyloidosis. Trypsin strongly induced aggregation of variants V30G and V30A, in each of which Val30 in the hydrophobic core of the monomer was mutated to less-bulky amino acids. Variants V30L and V30M, in each of which Val30 was mutated to bulky amino acids, also exhibited trypsin-induced aggregation. On the other hand, pathogenic variant I68L as well as the nonpathogenic V30I did not exhibit trypsin-induced aggregation. The V30G variant was extremely unstable compared with the other variants. The V30G mutation caused the formation of a cavity and the rearrangement of Leu55 in the hydrophobic core of the monomer. These results suggest that highly destabilized transthyretin variants are more susceptible to trypsin digestion.

中文翻译：

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胰蛋白酶诱导的转甲状腺素蛋白缬氨酸 30 变异体的聚集与遗传性淀粉样变性相关

转甲状腺素蛋白 (TTR) 淀粉样原纤维由全长 TTR 和从残基 50 附近开始的 C 端片段组成。然而，C 端片段产生的分子机制仍不清楚。在这里，我们研究了与遗传性淀粉样变性相关的 TTR 变异的胰蛋白酶诱导的聚集和尿素诱导的展开。胰蛋白酶强烈诱导变体 V30G 和 V30A 的聚集，其中单体疏水核心中的 Val30 突变为体积较小的氨基酸。变体 V30L 和 V30M（其中 Val30 突变为大氨基酸）也表现出胰蛋白酶诱导的聚集。另一方面，致病性变异 I68L 以及非致病性 V30I 没有表现出胰蛋白酶诱导的聚集。与其他变体相比，V30G 变体极其不稳定。 V30G突变导致空腔的形成以及单体疏水核心中Leu55的重排。这些结果表明高度不稳定的运甲状腺素蛋白变体更容易受到胰蛋白酶消化。